Manufacture of tanning extracts.



UNITED TATE DONALD STEWART, 0F INVERNESS, SCOTLAND MANUFACTWE 0F TANNING EXTBAUTS no. ceases.

To all whom it may concern:

M. A. Edin, a subject of the King of Great,

Britain, residing at 99 Ardross street, Inverness, Scotland, have invented new and useful Improvements in the Manufacture of Tanning Extracts, of which the following is a specification.

Several proposals have from time to time been made, some of Which have found practical application, to utilize the waste sulfite liquors of the paper pulp manufacture in the manufacture of tannin extracts. In some cases the sulfiteli uors have been the source of the tannin in tie extract; in other cases the sulfite li uors have been used in conjunction with 0t iertannin containing material or a tannin containing extract.

Hitherto it has always been regarded as necessary to subject the sulfite liquors or the product of treating other tannin containing material or a tannin containing extract with such sulfite liquor, to some chemical treatment prior to concentration by evaporation.

- Such chemical treatment was designed to eliminate some one or more constituents of the sulfite liquor whose presence nor to concentration was regarded as drsadvantageous. Careful investigation of the subject has revealed to me the fact that apart from a possible excess of iron the sulfite liq uors can be used in conjunction with tannin containing material or extract in' the manufacture of tanning extracts. I have as a result of my investigations established what has never been hitherto recognized (a) that the iron in the sulfite liquors is the only possiblv disadvantageous constituent thereof,

' arid (b) that even the presence of the iron in the sulfite liquors may within. limits be disregarded.

As the result of analyses which I have made to determine the chemical composition of the sulfite liquors which at present are available I have found that the percentage of iron (hereinafter to be always understood as calculated FeO) in the ash of such liquors varies considerably. In some cases it is as low as nearly four percent. and in others it is as high as nearly fourteen per cent, and this percentage may vary within even wider limits. In general my ex erience is that the sulfite liquors obtainable on the European continent, for exam Is the French and German liquors, genera ly contain a percentage of iron in the ash approximating to the Specification of Letters Patent.

1 Application filed. may 1?, 1967. Serial No. 3%,240.

Patented an. 12, was;

higher limit, and that the American and Canadian liquors contain a percent-age of iron in the ash approximating to the lower limit.

According to my present invention I select for the purpose of manufacturing tanning extracts sulfite liquors whose ash contains not more than say six per cent. of iron in the ash or by suitable chemical means as by the addition of milk of lime or caustic soda I preci itate so'much of the iron content of the su fite liquor that the ash from the filtered liquor contains only about six per cent. or less of iron therein and employ such filtered 1i nor in manufacturing tanning extracts or use for the purpose of tanning a bath composed as hereinafter described containing as one source of tannin sulfite liquor selected or treated as aforesaid.

I will now proceed to describe how in accordance with my present invention. I manufacture tanning extracts and prepare a bath for tanning.

Hemlock, mangrove, oak, chestnut or other tannin containing material, having been previously ground or suitably prepared for extraction, is placed in vats or pits suitably constructed, and I add sulfite liquors selected or treated as aforesaid either of the concentration as received from the factory or diluted with water. These liquors ,are passed successively through the various vats of tannin containing material, and as the temperature is raised they extract the tannin, and at the same time they have a bleaching effect. As the liquor percolates through the tannin containing material, certain gummy substances are filtered oil, and certain of the lime and i'ron salts which the liquors may contain are to a large extent eliminated by the process of percolation. The

resulting liquor is then put into a large set-- tling tank, Where difficultly soluble substances are allowed to settle. The clear liquor is then concentrated in vacuum pans, or by any other suitable method of concentration, until the liquor has reached a density suitable for transportpvhen it may be barreled, it is then ready for use in the tauyard. During the heating of the liquors in the concentrating pans an interaction takes place between the sulfites in the li uor and the tannin; the sulfurous' acid w ich is liberated having as stated above a slight bleaching effect upon the tannin improves the color of the resuiting fluid. I may make use of ox alic acid or any other suitable acid to blend further bleaching with the liquor to liberate more or less of the combined sulfurous acid, so as to get a action if desired.

As an alternative I treat a tanning extract with a sulfite liquor selected or treated as aforesaid. In such case the tanning extract is treated with the sulfite liquor in the manner described above in respect of a tannin containing material, 'i. e., the tanning extract and waste sulfite liquor are ut in a settling tank where diflicultly solu le substances are allowed to settle. liquor is then concentrated in vacuum pans or by any other suitable method of concentration until the liquor has reached a suitable density. As a further alternative I may blend sulfite liquors selected or treated as aforesaid direct with the aqueous solutions of hemlock, oak, chestnut or other tannin containing material in any suitable proportion, If these blends are to be used direct by the tanner without concentration I recommend the Warming of the liquor, so that a perfect blending of the solutions takes ace. I p What I claim is 1. The processof manufacturing tanning extracts and liquors, consisting in adding waste sulfitc liquor, whose ash contains not more than 6% of ironcalculated as heO, to tannin-containing material.

2. A tanning liquor or extract consisting ofa tanning extract and waste sulfite liquor whose ash contains-not more than- 6% of iron calculated as h'eO.

The clear ceases 1 3-; The process of manufacturing tanning extracts and li uors, consisting in removing from waste-su fite liquor the iron therein until the ash contains not more than 6% of iron calculated as heO, and adding such liquor to tannin-containing material.

4. The process of manufacturing tanning extracts and liquors, which consists in passing successively through vats or pits contaming tannin-containing material waste sulfite liquor Whose ash contains not more than 6% of iron calculated as MO.

5. The process ofmanufacturing tanning extracts and liquors, which consists in passing successively through vats or pits containing tannin-containing material waste sulfite liquor whose ash contains not more than 6%- of iron calculated as a co, and then settling out diflicultly soluble substances and concentrating the clear liquor.

, 6. The process of manufacturing tanning extracts and liquors, which consists in adding waste sulfite liquor Whose ash contains not more than 6% of iron calculated as h eO, to tannin extracts and settling out difiicultly soluble substances and concentrating the clear liquor.

7. A tanning extract consistin of an ex tract of hemlock and a Waste su fite liquor -whose ash contains not more than 6% of iron calculated as reO.

DONALD STEWART.

Witnesses:

. WILLIAM P. QUANN,

HENRY A. BoTHWELL. 

